Yes, the organization_id in rcv_transactions refers to the organization in which the receiving transactions are completed. The to_organization_id in rcv_shipment_lines will become the organization_id in rcv_transactions after completing the receipts for the given shipments.

What do you mean by "receiving transactions are completed"? if there are RECEIVE,ACCEPT and DELIVER transactions of an item, would it be the DELIVER transaction at which receiving will complete? if yes, then is it possible that we RECEIVE in one organization, ACCEPT in another and then DELIVER in some other?

It is not possible that we RECEIVE in one organization and ACCEPT/DELIVER in some other organization.

What I meant was that once the receipts are initiated for the shipments either just be RECEIVE (Incase of Standard or Inspection Routings) or RECEIVE & DELIVER (incase of DIRECT receipt routing), the organization_id would be the one in which the receiving transactions appear.